Copper Alloy

ABSTRACT

Alloys are demonstrated based on copper, which have additions of manganese and sulfur and/or calcium as well as additional elements. The copper alloys are free from tellurium and lead, and are distinguished by high electrical conductivity and good machinability.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a copper alloy, particularly a lead-free and tellurium-free copper alloy, as well as semifinished products made of such a copper alloy.

2. Description of the Related Art

In many fields of industry and technology, copper is an indispensable material because of its natural qualities. Especially when materials are required having the highest electrical and thermal conductivity, copper and copper alloys are of great importance. The use of pure copper, however, brings on difficulties if parts are to be processed in a metal-cutting manner. The high toughness of copper, which is particularly valued in chipless shaping, proves to be a disadvantageous material property in this instance. The cause for this is long chip formation, which impedes the operating sequence during drilling and turning, and leads to large wear of the cutting lips. On CNC-controlled, as well as on usual automatic lathes, pure copper is normally workable or processable only at uneconomically high costs in time, personnel and tooling.

Machinable copper materials are known having admixtures of lead, bismuth, sulfur or tellurium. As early as in U.S. Pat. No. 1,959,509 the favorable influence of alloying bismuth on the machinability of copper alloys was explained. The advantageous properties of tellurium in copper alloys may be seen in U.S. Pat. No. 2,027,807.

Lead and bismuth act as chip breakers in metallic form, sulfur and tellurium, on the other hand, act as an intermetallic phase in the form of copper sulfide (Cu₂S) or copper telluride (Cu₂Te). However, the low melting points of lead and bismuth restrict the hot ductility considerably, for instance, by extrusion, so that economical processability on conventional production devices cannot be taken for granted, or only in a limited way. In addition, there are health-related and environmentally hazardous considerations with respect to lead in copper alloys.

On the other hand, copper materials having the addition of sulfur or tellurium in the form of CuSP or CuTeP stand out by having a favorable combination of good machinability as well as a very high electrical and thermal conductivity. However, tellurium is particularly limited in its availability as a result of raw material scarcity, and is comparatively costly. Therefore, in response to an increasing resource scarcity of tellurium, an alternative would be desirable.

DESCRIPTION OF THE INVENTION

Accordingly, it is an object of the present invention to provide a copper alloy which, compared to the known copper alloys CuTeP and CuSP, has a machinability as well as cold-formability and hot ductility that is at least equal or better.

The objective is first attained, according to the present invention, claims 1-8, by an alloy based on copper, consisting of:

-   -   0.05 to 0.80 wt. % manganese (Mn),     -   0.10 to 0.80 wt. % sulfur (S),     -   optionally one or more elements selected from the group made up         of     -   0.002 to 0.05 wt. % phosphorus (P),     -   0.01 to 0.5 wt. % chromium (Cr),     -   0.01 to 0.5 wt. % aluminum (Al),     -   0.01 to 0.5 wt. % magnesium (Mg),     -   and     -   the remainder being copper (Cu) and unavoidable impurities.

A copper alloy is proposed, in accordance with the present invention, based on copper having the addition of manganese and sulfur, as well as accompanying elements, which can do without lead or tellurium, but demonstrates good machinability.

The copper alloy consists of copper, which has as alloying components 0.05 to 0.80 wt. % manganese (Mn), 0.10 to 0.80 wt. % sulfur (S), and optionally one or more elements selected from the group made up of 0.002 to 0.05 wt. % phosphorus (P), 0.01 to 0.05 wt. % Chromium (Cr), 0.01 to 0.5 wt. % aluminum (Al), 0.01 to 0.5 wt. % magnesium (Mg), besides unavoidable impurities.

A mixed phase, consisting of copper sulfide (Cu₂S) and manganese sulfide (MnS) acts as chip breaker in the CuSMn alloy according to the present invention.

Especially preferred, the manganese proportion amounts to 0.10 to 0.20 wt. %. Also preferred, there is a sulfur proportion, that is between 0.20 to 0.60 wt. %.

The object on which the present invention is based is furthermore attained by an alloy based on copper according to claims 9-12. It consists of 0.30 to 1.50 wt. % calcium (Ca), optionally one or more elements selected from the group which consists of 0.005 to 0.05 wt. % manganese (Mn), 0.005 to 0.05 wt. % sulfur (S), 0.002 to 0.05 wt. % phosphorus (P), 0.01 to 0.5 wt. % chromium (Cr), 0.01 to 0.5 wt. % aluminum (Al), 0.01 to 0.5 wt. % magnesium (Mg), as well as the remainder copper (Cu) and unavoidable impurities.

The calcium proportion in the previous copper alloy is preferably between 0.5 to 1.0 wt. %.

In the CuCa alloy, the forming eutectic phase Cu₅Ca acts as a chip breaker.

Phosphorus is used as a deoxidizer, which binds the free oxygen dissolved in the melt to itself, and thus avoids gas bubbles (hydrogen disease) and the oxidation of alloy components. Moreover, phosphorus is added to improve the flowing properties of the copper alloy during casting.

Manganese refines the grain and, in combination with sulfur, improves the machinability.

Aluminum increases the hardness and yield strength without reducing the toughness. Aluminum is an element which improves the strength, machinability and resistance to abrasion, as well as the resistance to oxidation at high temperatures.

Chromium and manganese are used to improve the resistance to oxidation at high temperatures. In this instance, particularly good results are obtained if they are mixed with aluminum, so as to achieve a synergy effect.

The two copper materials CuSMn and CuCa proposed in the present invention have a machinability which is equal to or better than that of CuSP. During experiments, a machinability index of 90% was ascertained for CuSMn, 86% for CuCa and 76 and 79% for the reference materials CuTeP and CuSP.

The materials have an electric conductivity that is between 35 and 55 MS/m, particularly in a range of 48 to 53 MS/m. Furthermore, the copper alloys proposed in the present invention are free from toxic alloying elements and are cost-effective, since the alloying elements are available cost-effectively. In addition, we should emphasize the importance of the scraps being reusable. A special criterion of the two proposed copper alloys is that workability using conventional production and processing machines is possible, and in particular, the alloys have both a sufficient cold-formability and also a very good hot ductility.

Therefore, using the proposed copper alloys, semifinished products in the form of rolled products, extruded/drawn products, forged products or cast products are made available.

Exemplary Embodiments and Comparative Observations

With the aid of two exemplary embodiments, let us explain the advantageous properties according to the present invention of the new lead-free and tellurium-free alloys, as compared to the known and standardized materials CuTeP (=EN alloy CW118C, ASTM alloy C14500) and CuSP (=EN alloy CW114C, ASTM alloy C14700).

In a crucible induction furnace, CuSMn, CuCa and the reference materials CuTeP and CuSP respectively were melted and cast to extrusion billets in a continuous casting method. The composition of the materials is reproduced in Table 1. The composition of CuSMn corresponds to claims 1-8, CuCa fulfills claims 9-12. The composition of the reference materials CuTeP and CuSP corresponds to the specifications of EN and ASTM. The continuously cast round billets were extruded in an extruding press at a heating-up temperature of 850° C. without problems to bars and were subsequently drawn at a cross sectional reduction of 10 to 15% to a final diameter of 35 mm. Having the cross sectional reduction of 10 to 15%, the most frequently supplied temper R250 for machinable copper according to EN 12164 or H02 according to ASTM B301 is achieved. Table 2 shows characteristic mechanical properties and the Brinell hardness and specific electrical conductivity of the bars in the finished drawn temper. The test results show, that the new materials according to the present invention, using the standard materials CuTeP and CuSP have comparable mechanical characteristics and an equally good electrical conductivity as the standard materials CuTeP and CuSP. Material CuSMn, based on the even more favorable strength/fracture elongation combination compared to standard material CuSP, still has the advantage of better cold-formability (e.g. for producing “hammered” torch tips).

Machinability Investigations

With regard to the bars listed in Table 2, comparative machinability tests in the form of drilling tests were carried out. Processing by drilling was given the advantage over processing by turning or thread cutting, because the production of small bores (such as in torch lips) represents the most difficult chip-cutting processing form. If a material demonstrates positive results in this instance, processing by turning or thread-cutting will also not represent a problem.

For the drilling tests, the following parameters were used, that are usual in modern processing machines:

-   -   drilling tool: 2 mm Φ hard metal drill having inner cooling         -   tip coated with AlTiN         -   type Gühring WNRN15XD     -   drilling strategy: at end face apply 45 bores into bar sections:         -   cutting speed: 100 m/min         -   feed function: 0.04 mm/revolution         -   drilling depth 33 mm         -   inner cooling drill: emulsion 40 bar

The following were valued:

-   -   the chip form in accordance with steel test sheet 1178-90     -   the average chip mass via weight measurement of 100 chips each     -   tool wear as flank wear after 270 bores     -   required average feed function force     -   bore quality in the light of criteria:         -   cylindricity (conicity) of bore over the length         -   roundness of the bore over the circumference         -   diameter deviation over the length         -   roughness R₂ of the boring surface

In order to make possible a quantitatively comparative valuation of the materials to the reference materials, the single measurement results were valued using a point system of 0 to 10 points, 0 points meaning extremely bad and 10 points meaning optimal=very good.

The individual valuations were added, a maximum of 80 points being achievable. This overall valuation of the machinability shall be defined here as machinability index, where 80 points then correspond to a maximum achievable machinability index of 100%. The results of these investigations are listed in table 3. The new materials according to the present invention, CuCa and CuSMn, in comparison to the reference materials, achieve the following machinability indices:

CuSMn: 90%

CuCa: 86%

CuTeP: 76%

CuSP: 79%

To clarify the good brittle machinability of all materials, FIG. 1 shows the drilling chips from the machinability investigations. The somewhat longer helical chip pieces occur only sporadically. The very thorough and effortful machinability investigations have shown that the materials according to the present invention are at least equivalent in machinability to reference materials CuSP and CuTeP that have been available up to now, or even have slight advantages.

In careful investigations, the inventors have created a copper material which supplements the current selection of available like with CuTeP and CuSP, and which has the following quality features:

-   -   machinability equal to or better than CuTeP/CuSP;     -   electrical conductivity ≧35 MS/m;     -   free from toxic alloying elements;     -   cost-effective availability of the alloying elements;     -   reusability of the scrap;     -   processability using conventional production steps and machines.

In the investigations, each alloying element aluminum (Al), calcium (Ca), cobalt (Co), chromium (Cr), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum (Mo), nickel (Ni), tin (Sn) and zinc (Zn) was tested in combination with sulfur (S) and calcium (Ca) as a single addition to copper with respect to the achievable electrical conductivity and machinability. The well-established materials CuSP and CuTeP were used as comparative samples for the machinability tests. Qualitatively valued was the shape of the chips during the drilling of 3 mm holes and the appearance of drill fractures.

The desired material properties or property combinations were achieved by alloying manganese, specifically in a proportion of 0.05 to 0.80 wt. %, preferably 0.10 to 0.30 wt. %, particularly 0.10 to 0.20 wt. %, as well as sulfur in a proportion of 0.10 to 0.80 wt. %, particularly 0.20 to 0.60 wt. %.

Moreover, it could be determined that the desired material properties in an alloy based on copper could be achieved, which contains as an alloy component calcium having a proportion of 0.30 to 1.50 wt. %, preferably between 0.5 and 1.0 wt. %.

It was recognized as essential to the present invention that the two copper materials CuSMn and CuCa that were pointed out have the aforementioned independent chip-breaking phases, namely the mixed phase consisting of Cu₂S and MnS and the eutectic phase Cu₅Ca.

In the processing and testing of material samples of the copper alloys according to the present invention, it was shown that particularly the alloy CuSMn had a hot ductility and cold formability that was comparable to, or even slightly better than copper alloy CuSP or copper alloy CuTeP.

TABLE 1 Composition of the Materials CuSMn, CuCa According to the present Invention and the Reference Materials CuTeP and CuSP Composition in wt. % Unavoidable Material Cu Te S Mn Ca P impurities CuSMn 99.50 / 0.30 0.18  / 0.007 0.01 CuCa 99.22 / 0.005 0.007 0.73 0.02 0.02 CuTeP 99.53 0.44 / / / 0.007 0.02 Setpoint balance  0.4-0.7 / / / 0.003- ≦0.1 values EN- 0.012 CW118C Setpoint +Te ≧ 99.90 0.40-0.7 / / / 0.004- / values ASTM- 0.012 C14500 CuSP 99.65 / 0.31 / / 0.005 0.03 Setpoint balance / 0.2-0.7 / / 0.003- ≦0.1 values EN- 0.012 CW114C Setpoint +S ≧ 99.90 / 0.20-0.50 / / 0.002- / values ASTM- 0.005 C14700

TABLE 2 Mechanical and Technological Properties of the Materials CuSMn and CuCa According to the Present Invention and Reference values of CuTeP und CuSP in the Drawn Half-hard Temper (R250 According to EN 12164 and Temper H02 According to ASTM B301) Tensile 0.2% Yield Elongation Brinell Specific el. conductivity strength Strength after Fracture hardness in soft temper at 20° C. Material R_(m) (MPa) R_(p0.2) (MPa) A (%) HBW2.5/62.5 (MS/m) (% IACS) CuSMn 265 245 20 85 53.0 91.5 CuCa 269 261 13 97 52.5 90.5 CuTeP 286 257 18 88 53.0 91.5 CuSP 269 263 14 85 52.5 90.5 Setpoint ≧250 ~200 ≧7 ~90 / / values for CuTeP + CuSP: EN 12164 R250 Setpoint ≧260 ≧205¹⁾ ≧12 / / CuTeP ≧ 85.0 values for ¹⁾ 0.5% CuSP ≧ 90.0 C14500 + Yield C14700 strength ASTM B301 under load HO2

TABLE 3 Results of Machinability Investigations (including valuation) Drilling quality Roundness Machin- (diameter ability Average deviation Diameter Overall index in Flank wear feed Cylindricity over the deviation Rough- valua- % Average after 270 function (conicity of circum- over the ness tion (80 P = chip mass bores force the bore) ference) length R_(z) Sum 100%) Material Chip type μg μm N μm μm μm μm points % CuSMn Spiral chips, 90 20 40 20 5 0 1 (72) 90 spiral chip (8 P) (8 P) (9 P) (9 P) (10 P) (10 P) (10 P) pieces helical chip pieces (8 P) CuCa Discontinuous 50 17 70 10 5 0 3 (69) 86 chips (10 P) (10 P) (10 P) (4 P) (10 P) (10 P) (10 P) (5 P) CuTeP Spiral chips, 110 20 35 50 10 20 1 (61) 76 spiral chip (8 P) (8 P) (10 P) (6 P) (5 P) (6 P) (10 P) pieces helical chip pieces (8 P) CuSP Spiral chips, 90 28 50 30 5 10 1 (63) 79 spiral chip (8 P) (4 P) (7 P) (8 P) (10 P) (8 P) (10 P) pieces helical chip pieces (8 P) drill fractures did not occur with any material 

What is claimed is:
 1. An alloy based on copper, comprising: 0.05 to 0.80 wt. % manganese (Mn), 0.10 to 0.80 wt. % sulfur (S), and a remainder being copper (Cu) and unavoidable impurities.
 2. The alloy based on copper as recited in claim 1, further comprising at least one additional element selected from the group consisting of: 0.002 to 0.05 wt. % phosphorus (P), 0.01 to 0.5 wt. % chromium (Cr), 0.01 to 0.5 wt. % aluminum (Al), and 0.01 to 0.5 wt. % magnesium (Mg).
 3. The alloy based on copper as recited in claim 1, wherein the manganese proportion is from 0.10 to 0.30 wt. %.
 4. The alloy based on copper as recited in claim 1, wherein the manganese proportion is from 0.10 to 0.20 wt. %.
 5. The alloy based on copper as recited in claim 2, wherein the manganese proportion is from 0.10 to 0.30 wt. %.
 6. The alloy based on copper as recited in claim 1, wherein the sulfur proportion is from 0.20 to 0.60 wt. %.
 7. The alloy based on copper as recited in claim 2, wherein the sulfur proportion is from 0.20 to 0.60 wt. %.
 8. The alloy based on copper as recited in claim 3, wherein the sulfur proportion is from 0.20 to 0.60 wt. %.
 9. An alloy based on copper, comprising: 0.30 to 1.50 wt. % calcium (Ca), and a remainder being copper (Cu) and unavoidable impurities.
 10. The alloy based on copper as recited in claim 9, further comprising at least one additional element selected from the group consisting of: 0.005 to 0.05 wt. % manganese (Mn), 0.005 to 0.05 wt. % sulfur (S), 0.002 to 0.05 wt. % phosphorus (P), 0.01 to 0.5 wt. % chromium (Cr), 0.01 to 0.5 wt. % aluminum (Al), and 0.01 to 0.5 wt. % magnesium (Mg),
 11. The alloy based on copper as recited in claim 9, wherein the calcium proportion is from 0.5 to 1.0 wt. %.
 12. The alloy based on copper as recited in claim 10, wherein the calcium proportion is from 0.5 to 1.0 wt. %.
 13. The alloy based on copper as recited in claim 1, having an electrical conductivity of 35 to 55 MS/m.
 14. The alloy based on copper as recited in claim 2, having an electrical conductivity of 35 to 55 MS/m.
 15. The alloy based on copper as recited in claim 9, having an electrical conductivity of 35 to 55 MS/m.
 16. The alloy based on copper as recited in claim 10, having an electrical conductivity of 35 to 55 MS/m.
 17. The alloy based on copper as recited in claim 1, having an electrical conductivity from 48 to 53 MS/m.
 18. The alloy based on copper as recited in claim 2, having an electrical conductivity from 48 to 53 MS/m.
 19. The alloy based on copper as recited in claim 1, having a machinability index of 80% to 95%.
 20. The alloy based on copper as recited in claim 2, having a machinability index of 80% to 95%.
 21. A semifinished material made of an alloy as recited in claim 1 in the form of a rolled product.
 22. A semifinished material made of an alloy as recited in claim 2 in the form of a rolled product.
 23. A semifinished material made of an alloy as recited in claim 1 in the form of an extruded/drawn product.
 24. A semifinished material made of an alloy as recited in claim 2 in the form of an extruded/drawn product.
 25. A semifinished material made of an alloy as recited in claim 1 in the form of a forged product.
 26. A semifinished material made of an alloy as recited in claim 2 in the form of a forged product.
 27. A semifinished material made of an alloy as recited in claim 1 in the form of a cast product.
 28. A semifinished material made of an alloy as recited in claim 2 in the form of a cast product. 